The top-seeded Federer needs to reach the semi-finals to return to the top spot for the first time since 4 November 2012. But the 36-year-old Swiss might have to beat his surging countryman Stan Wawrinka in the quarter-finals.

Wawrinka is the fifth seed at the ATP World Tour 500 event, and appears to be well on his way to regaining top form. Wawrinka is in the semi-finals this week at the Diema Xtra Sofia Open in Bulgaria. Federer will face a qualifier in the first round and will meet either German Philipp Kohlschreiber or Russian Karen Khachanov in round two.

Federer first rose to the top spot 14 years ago on 2 February 2004 and holds the record for most weeks spent at No. 1 (302). If he makes the semi-finals, he will become the oldest No. 1, eclipsing Andre Agassi (33).

Federer moved to within 155 points of World No. 1 Rafael Nadal after claiming his 20th Grand Slam title at the Australian Open last month. The Swiss right-hander has previously played the ATP World Tour 500 tournament in Rotterdam eight times, taking the title in 2005 and 2012.

* Nadal is guaranteed to stay No. 1 until at least 18 February 2018.
^ Federer is 36 years old as of 19 February 2018.

Nadal, who is not scheduled to play again until Acapulco in the last week of February, has held No. 1 for the past 25 weeks (since 21 August 2017). The Spaniard has been No. 1 in the ATP Rankings a total of 166 weeks since first taking over on 18 August 2008. Nadal is seventh all-time in most weeks at No. 1 in the history of the ATP Rankings (since 1973).

* Nadal is guaranteed to stay No. 1 until at least 18 February 2018.^ 19 February 2018 marks 14 years, 17 days since Federer debuted at No. 1 on 2 February 2004.

Federer has a 23-6 record in Rotterdam. In addition to his two titles, he reached the final in 2001 and semi-finals in 2003. His last appearance at the Rotterdam Ahoy stadium in The Netherlands was 2013, when he lost in the quarter-finals to Julien Benneteau.

* February 19, 2018 marks five years, 106 days since Federer was last No. 1 on 4 November 2012.

Should Federer make the semi-finals, his path hardly gets easier. Alexander Zverev could await in the last four, and on the opposite side of the draw, fourth seed David Goffin, who beat Federer at the 2017 Nitto ATP Finals, lurks along with World No. 4 Grigor Dimitrov, the second seed at the ATP World Tour 500 event.